Parties loyal to Mr. Akayev officially won 90 percent of the votes in recent parliamentary elections. But the rapid collapse of his security forces and government after about 10,000 opposition supporters massed in Bishkek, the country's northern capital, Thursday suggests a very different reality.

"Akayev's 14 years in power have been a time of mass impoverishment for the people," says Sanobar Shematova, a Kyrgyz journalist who writes for the Russian daily Izvestia. "This revolt spread to the capital from the poorest regions of the country, where people are sick and tired of the corrupt authorities," and needed only a spark to set them off, she says.

Kyrgyzstan's upheaval will echo loudly in the corridors of power throughout the former USSR, experts say. Many post-Soviet governments, including Russia, share similar features to the regimes that have fallen to angry crowds in Georgia, Ukraine, and now Kyrgyzstan, in the past 18 months.

"Those regimes landed somewhere between authoritarianism and democracy," says Dmitry Trenin, a regional expert with the Carnegie Center in Moscow. "Greedy and stupid elites disregarded the needs of the population, enriched themselves, and never noticed the discontent spreading in their own societies. More of these revolts are certainly possible in future."

Many worry that the deeply fragmented opposition, which lacks a central leader, may prove incapable of utilizing the power that has fallen into its hands with Akayev's flight. Thursday the Russian independent radio station Ekho Moskvi reported that Akayev was on a plane headed for Moscow.

Earlier in the day about 1,000 protesters cleared riot police from their positions outside the fence protecting the building, and about half entered through the front. Others smashed windows with stones.

"The authorities have proven very weak, but the opposition is not a mature force capable of ruling," says Ms. Shematova. Mr. Trenin adds: "Akayev is basically finished. But should the opposition fail to hold together it could succumb to the Islamist challenge. I am watching Kyrgyz events with great apprehension."

As in Georgia in 2003 and Ukraine last December, the trigger for Kyrgyzstan's upheaval was an election widely viewed as fraudulent. Parliamentary polls that ended March 13 returned a huge majority of Akayev supporters - including the president's son and daughter - but several opposition leaders were banned from running, several independent newspapers were shut down, and international monitors reported serious irregularities on election day.

Kyrgyzstan's Supreme Court Thursday declared the nation's controversial parliamentary elections invalid, the ITAR-Tass news agency reported. The Kyrgyz parliament was to reconvene after the court's ruling. Members of the opposition People's Movement of Kyrgyzstan say they hope to hold new elections this fall.

Last week opposition forces seized four regions in the impoverished and ethnically diverse south of Kyrgyzstan, including the key centers of Osh and Jalalabad. Police offered only token resistance in most cases - an early sign, experts say, of the fundamental weakness of the Akayev regime.

"It's clear the majority of people, and even the security forces, were alienated from Akayev and his corrupted regime," says Vitaly Naumkin, an expert with the independent Center for Strategic and Political Studies in Moscow. "His own personal lack of determination was a reflection of the deeper lethargy of his government."

Many of those who rallied in Bishkek Thursday had been bussed in across the Tien Shan mountains from the country's southern zone. But observers say the demonstrators were greeted positively by much of the local population, even though Bishkek - like much of Kyrgyzstan's northern zone - is ethnically Kyrgyz, more prosperous and, until now, more solidly pro-Akayev.

Little is known about the opposition leaders who might come to power in coming days. Some of them are disaffected former officials of Akayev's regime, including one-time Foreign Minister Roza Otunbayeva and ex-prime minister Kurmanbek Bakiyev.

The only leader that experts describe as a potential unifying figure is Felix Kulov, an ex-KGB official and Akayev's former vice president who was jailed on what the opposition alleges were trumped-up charges of corruption and power abuse in 2001. Demonstrators released Mr. Kulov from jail Thursday. "Kulov is a very powerful, even charismatic leader, with a broad political base," says Mr. Naumkin. "He is the only one who might conceivably unite the opposition and forge a single leadership."

Ekho Moskvi quoted Kulov as saying, "We must carry out a peaceful and constitutional transition of power in Kyrgyzstan. This has been a justified popular revolt," he said.

Akayev, a former physicist, was acclaimed as a forward-looking reformer when he was elected president of Kyrgyzstan in 1990. For many years his regime was considered one of the most liberal in the former Soviet Union. But he grew increasingly autocratic, allowed corruption and nepotism to flourish, and alienated leading members of rival clans. In 2003 he moved to expand his presidential authority, which many critics took as a signal he intended to remain in power after his constitutional term expires next October.